Conventional x-ray imaging focuses on attenuation as a physical quantity to provide contrast between various types of human tissue. More recently, other imaging techniques like dual-energy imaging or phase contrast imaging provide information about different physical quantities like the electron density, refractive index decrement, or scattering cross sections of the imaged tissues. It appears that image contrast (that is, the relative differences between image elements) can be more pronounced in either of the attenuation based imaging or refractive index based imaging and it appears that no general statement can be made as to which one of the two imaging techniques is the better one.